Use of tin derivatives as catalysts for transforming carbamates, carbamate compositions comprising said catalyst and method for transforming carbamates

ABSTRACT

The invention concerns the use as catalyst for transforming carbamates of compounds corresponding to the general formula (I): —Sn (X) (X′) wherein: X′ is selected among chloride, bromide, iodide, thiocyanate radicals, sulphonate radicals, advantageously perfluorinated on the carbon bearing the sulphonate function; X is selected among the values of X′ and among radicals of formula Y-Z; Y is selected among the chalcogen groups, advantageously light (that is oxygen and sulphur); Z is selected in the group consisting of trisubstituted tin, monosubstituted zinc, and the oxygenated acid radicals after ignoring the OH function. The invention is applicable to the coating industry.

[0001] A subject matter of the present invention is noveltranscarbamation catalysts. The invention relates more specifically tothe use of novel tin-based catalysts.

[0002] Because of their high reactivity and their relative toxicity,isocyanates are often used in a derived form or in a masked form. Thisderived form or this masked form exhibits the disadvantage correspondingto its advantages, that is to say that it is not very reactive, andconsequently requires the use of catalysts in order for the reaction tobe able to take place at temperatures acceptable in industry.

[0003] Masked isocyanates can be used in all the applications ofisocyanates, namely paints, varnishes and more generally coatings,adhesives, and some specialty polymers.

[0004] The most widely used catalysts are dialkyltin alkanoates, themost well known of which is dibutyltin dilaurate. However, for someapplications, dibutyltin dilaurate exhibits an insufficient activity andconsequently it is necessary to use it at very high concentrations.

[0005] These transcarbamation catalysts make it possible to preparepolyurethanes, in particular aliphatic polyurethanes.

[0006] This is why one of the aims of the present invention is toprovide a transcarbamation catalyst which is more active than dibutyltindilaurate.

[0007] Another aim of the present invention is to provide a catalyst ofthe preceding type which can also be used for the carbamation of oximes.

[0008] Another aim of the present invention is to provide atranscarbamation catalyst which can be used to convert carbamates ofmethanol and carbamates of primary alcohols.

[0009] These aims, and others which will become apparent subsequently,are achieved by means of the use as transcarbamation catalysts ofcompounds of following general formula (I):

[0010] where:

[0011] X′ is chosen from chloride, bromide, iodide or thiocyanateradicals or sulfonate radicals, advantageously perfluorinated on thecarbon carrying the sulfonate functional group;

[0012] X is chosen from the values of X′ and from radicals of formulaY-Z;

[0013] Y is chosen from the group of chalcogens, advantageously lightchalcogens (that is to say, oxygen and sulfur);

[0014] Z is chosen from the group consisting of trisubstituted tin,monosubstituted zinc and residues of oxygen-comprising acids, the OHfunctional group not being included.

[0015] The compounds of this family exhibit a particularly advantageouscatalytic activity. Among the compounds of the present family, thecompounds where X′ is a relatively heavy halide anion, that is to saychloride, bromide or iodide, should be more particularly indicated. Thefirst two mentioned are preferred, in particular bromide. Relativelybulky anions, the associated acid of which exhibit a strong or verystrong acidity, also give good results, in particular if they exhibitgood solubility in fats. Mention may be made, among the acids givinganions which bring about good properties, of those which exhibit apK_(a) at most equal to 2. Mention may be made, among these acids, ofsulfonic acids or stable carboxylic acids carrying anelectron-withdrawing functional group on the carboxylic carbon, so thatthe PK_(a) corresponds to the above restriction. Mention may inparticular be made of perfluoroacetic acid.

[0016] Another acid which gives particularly satisfactory results isthiocyanic acid or more specifically its anion, thiocyanate. Thepreferred sulfonic acids are those for which the carbon carrying thesulfonic functional group carries at least two fluorine atoms.

[0017] Mention should be made, among the most active members of thefamily defined by the formula (I), of symmetrical compounds, that is tosay those where X corresponds to the formula Y-Z and where Z and X′—Sn—are symmetrical, so that the chalcogen atom carries two identicalradicals. In the formula (I), the “free” bonds of the tin areadvantageously connected to hydrocarbonaceous groups, that is to saycomprising hydrogen and carbon (but not necessarily comprising onlyhydrogen and carbon). These hydrocarbonaceous groups are advantageouslychosen from aryls or alkyls (the latter being taken from alcohols, saidalcohol functional group of which is not included); alkyls arepreferred.

[0018] The combined radicals must be such that the carbon number of thecompounds of formula (I) does not comprise at most 50 carbon atoms,preferably 25 carbon atoms.

[0019] The “free” bond of the zinc is generally connected to ahydrocarbonaceous compound, advantageously to the anion of anoxygen-comprising acid, advantageously a carboxylic acid.

[0020] These catalysts are advantageously used in an amount at leastequal to 0.5% and at most equal to 5% as carbamate functional groupequivalent, preferably between 1% and 2%.

[0021] The transcarbamation reaction depends on the alcohols andcarbamates used. However, it is between 100 and 200° C., preferablybetween 120 and 180° C. The carbamates used are those resulting from thereaction of an isocyanate functional group with a hydroxyl functionalgroup. Mention should be made, among hydroxyl functional groups, ofalcohol functional groups, in particular those of alcohols which arevolatile at the reaction temperature (boiling point at atmosphericpressure) and more particularly methanol.

[0022] Among the other hydroxyl functional groups which may be mentionedas exhibiting a specific advantage, phenol functional groups, hydroxylfunctional groups grafted to a nitrogen atom, such as hydroxyimides, oroximes.

[0023] The alcohols which are substituted for these hydroxylatedderivatives are advantageously polyols (especially di- and/or triols),advantageously primary polyols.

[0024] The molecular masses can vary within a wide range according tothe form of the coating used. The molecular masses are relatively high,it being possible for them to range approximately up to 20 000 when thecatalysts according to the present invention are employed in a powderpaint, on the other hand, for more conventional applications, thepolyols rarely exceed a molecular mass of approximately 3 000.

[0025] The molecular masses referred to are number-average molecularmasses M_(n) and are defined by the gel permeation technique known to “aperson skilled in the art”. More specifically, the molecular mass isdetermined by gel permeation chromatography (GPC). The technique usestwo polystyrene gels (Ultrastyrogel® at 10⁴ and 500 Å) as gels, THF assolvent and sulfur as standards.

[0026] The isocyanates giving rise or corresponding to the carbamateswhich are preferred are at least partially aliphatic isocyanates, thatis to say that the isocyanate functional group under consideration isconnected via the nitrogen to the backbone of the isocyanate molecule bya carbon atom possessing sp³ hybridization.

[0027] In addition, it is desirable, in the structure of the isocyanate[lacuna] or monomers (that is to say, isocyanates which are oligomerizedsubsequently, the commonest of which are hexamethylene diisocyanate andthe compound denoted by the term isophorone diisocyanate, or IPDI), forthe part of the backbone connecting two isocyanate functional groups tocomprise at least one polymethylene sequence (CH₂)_(π) where πrepresents an integer from 2 to 10, advantageously from 4 to 8. Thispreference affects the mechanical performance. When there are severalsequences, the latter can be alike or different. In addition, it isdesirable, in a monomer, for these polymethylene sequences to be free torotate and therefore exocyclic. When prepolymers, or oligomers,resulting from more than one monomer are used, it is desirable for thecondition relating to this polymethylene sequence to be found in atleast one of these monomers.

[0028] The preferred polyisocyanates are those which exhibit at leastone aliphatic isocyanate functional group. In other words, at least onemasked isocyanate functional group according to the invention isconnected to the backbone via a carbon of sp³ type advantageouslycarrying a hydrogen atom, preferably two. It is desirable for saidcarbon of sp³ type to be itself carried by a carbon of sp³ typeadvantageously provided with one and preferably two hydrogen atoms, thisbeing in order to avoid the isocyanate group under consideration beingin the neopentyl position. In other words, it is advisable to choose, asmonomer (which monomers generally carry two isocyanate functionalgroups), at least one compound which carries at least one aliphatic[lacuna] functional group which is neither secondary nor tertiary, norneopentyl.

[0029] In the case of a mixture obtained from several (in general two)types of monomers, it is preferable for that or those of the monomerswhich correspond to the above conditions and/or (advantageously “and”)to the condition with regard to the presence of polymethylene sequence(CH₂)_(π) to represent at least ⅓, advantageously ½, preferably ⅔, ofthe masked isocyanate functional groups. Thus, during the studyaccording to the present invention, excellent results were obtained withmixtures comprising ⅔ of HMDT (hexamethylene diisocyanate “trimer”) withIPDI or IPDT (IPDI “trimer”), the two being masked according to theinvention (nBDI, norbornane diisocyanate, and its trimer are similar).

[0030] Of course, preference is given to the case where all theisocyanates are aliphatic and also correspond to the above criterion.

[0031] According to the present invention, the masked isocyanate, pureor as a mixture, results from a polyisocyanate, that is to say having atleast two isocyanate functional groups, advantageously more than two(possibilities of fractional values since it generally relates to amixture of more or less condensed oligomers), which itself generallyresults from a precondensation or from a prepolymerization of anindividual diisocyanate (sometimes described as “monomer” in the presentdescription).

[0032] The average molecular mass of these prepolymers or of theseprecondensates is generally at most equal to 2 000 (one significantfigure), more commonly to 1 000 (one significant figure, preferablytwo).

[0033] Thus, among the polyisocyanates used for the invention, mentionmay be made of those of the biuret type and those for which the di- ortrimerization reaction has resulted in four-, five- or six-memberedrings. Among the six rings, mention may be made of the isocyanuric ringsresulting from a homo- or hetero-trimerization of various diisocyanatesalone, with other isocyanate(s) [mono-, di- or polyisocyanate(s)] orwith carbon dioxide gas; in this case, a nitrogen of the isocyanuricring is replaced by an oxygen. The oligomers comprising isocyanuricrings are preferred.

[0034] Mention should be made, among the most advantageous monomers, of,on the one hand, those which exhibit a polymethylene sequence as definedabove which is exocyclic, obviously including noncyclic, among which maybe mentioned tetramethylene diisocyanate optionally substituted by analkyl group, advantageously of at most four carbon atoms, preferably ofat most two carbon atoms; pentamethylene diisocyanate optionallysubstituted by an alkyl group, advantageously of at most four carbonatoms, preferably of at most two carbon atoms, and hexamethylenediisocyanate. Mention may be made, as monomers of cycloaliphatic naturewhich are preferably used in combination with isocyanates havingexocyclic or noncyclic polymethylene sequences, of the monomers and thecompounds resulting from the monomers below:

[0035] the compounds corresponding to the hydrogenation of the aromaticring or rings carrying the isocyanate functional groups of aromaticisocyanate monomers, and in particular TDI (toluene diisocyanate) andbiphenyl diisocyanates, the compound known under the abbreviation H₁₂MDIand the various BICs [bis(isocyanatomethylcyclohexane)]; and especially

[0036] norbornane diisocyanate, often known by its abbreviation NBDI;

[0037] isophorone diisocyanate or IPDI or3-isocyanatomethyl-3,5-trimethylcyclohexyl isocyanate.

[0038] Another subject matter of the present invention is maskedisocyanate compositions, the isocyanates being masked in the form ofcarbamates (lato sensu, that is to say the functional groupscorresponding to the sequence —N(R)—CO—O— where R is a hydrocarbonaceousradical, generally an alkyl radical, indeed even an aryl radical, ormore frequently a hydrogen), additionally comprising a catalyst offollowing general formula (I):

[0039] where:

[0040] X′ is chosen from chloride, bromide, iodide or thiocyanateradicals or sulfonate radicals, advantageously perfluorinated on thecarbon carrying the sulfonate functional group;

[0041] X is chosen from the values of X′ and from radicals of formulaY-Z;

[0042] Y is chosen from the group of chalcogens, advantageously lightchalcogens (that is to say, oxygen and sulfur);

[0043] Z is chosen from the group consisting of trisubstituted tin,monosubstituted zinc and residues of oxygen-comprising acids, the OHfunctional group not being included.

[0044] These isocyanates, masked in the form of carbonates, will bedenoted in the continuation of the description under the term ofcarbamates.

[0045] These compositions, which can be used in the paint industry andmore generally the coating industry, including adhesives, generallycomprise, in addition, alcohols or apolyalcohols, or polyols which aredescribed above.

[0046] These alcohol functional groups are advantageously primaryalcohol functional groups.

[0047] This is because primary alcohols generally react more rapidlythan secondary alcohols. The carbamates described above areadvantageously carbamates of hydroxylated compounds chosen from alcoholswhich are volatile at a temperature at least equal to 150° C. and fromhydroxylated masking agents. The hydroxylated masking agents, when theyare not alcohols, even lato sensu, that is to say vinyl alcohols orphenols, are generally compounds comprising the —N—O—H bond. In otherwords, they are essentially compounds where the hydroxyl functionalgroup is carried by the nitrogen. Mention may be made, among thefamilies of these compounds, of hydroxyimides and oximes, in particularthe oximes targeted by the European patent application (confers theapplication on behalf of the Applicant Company published under thenumber 0 869 982).

[0048] Oximes and hydroxyimides constitute a family of commonly usedmasking agents.

[0049] Another family of masking agents exhibiting a number ofadvantages is composed of phenols, advantageously exhibiting anelectron-withdrawing functional group on the ring (see in particular theEuropean patent application on behalf of the Applicant Company publishedunder No. 0 680 984 and the international application published underNo. 0 998 510).

[0050] When they are used as paint binder, the compositions comprise theusual additives for this use.

[0051] The present invention is also targeted at a transcarbamationprocess where use is made, as transcarbamation catalyst, of thecompounds of formula (I):

[0052] where:

[0053] X′ is chosen from chloride, bromide, iodide or thiocyanateradicals or sulfonate radicals, advantageously perfluorinated on thecarbon carrying the sulfonate functional group;

[0054] X is chosen from the values of X′ and from radicals of formulaY-Z;

[0055] Y is chosen from the group of chalcogens, advantageously lightchalcogens (that is to say, oxygen and sulfur);

[0056] Z is chosen from the group consisting of trisubstituted tin,monosubstituted zinc and residues of oxygen-comprising acids, the OHfunctional group not being included.

[0057] Advantageously, one of the X′ or X groups is chosen fromsulfonates perfluorinated on the carbon carrying the sulfonatefunctional group. These sulfonates advantageously correspond to theformula below:

EWG-(CX₂)_(p)—

[0058] where:

[0059] the X groups, which are alike or different, represent a chlorine,a fluorine or a radical of formula C_(n)F_(2n+1) with n an integer atmost equal to 5, preferably to 2, with the condition that at least oneof the X groups is fluorine, fluorine advantageously carried by thecarbon connected to the sulfur;

[0060] p represents an integer at most equal to 2;

[0061] EWG represents an electron-withdrawing group (that is to say,σ_(p) greater than zero, advantageously than 0.1, preferably than 0.2),the possible functional groups of which are inert under the conditionsof the reaction, advantageously fluorine or a perfluorinated residue offormula C_(n)F_(2n+1) with n an integer at most equal to 8,advantageously to 5, the total carbon number of Rf advantageously beingbetween 1 and 15, preferably between 1 and 10.

[0062] Advantageously, X and X′ are chosen from the compounds of aboveformula.

[0063] These catalysts make it possible to carry out the reaction attemperatures below 200° C., advantageously below 180° C.

[0064] Generally, in order to obtain satisfactory kinetics, it isadvisable to be at a temperature at least equal to 100° C., preferablyat a temperature at least equal to 120° C.

[0065] The following nonlimiting examples illustrate the invention.These examples, in order to avoid any interaction problems, relatedsubstantially to monofunctional isocyanates. n-Hexyl isocyanate wasused.

EXAMPLE

[0066] General Procedure:

[0067] Choice of the Reaction Model

[0068] The choice focused on the use of aliphatic isocyanates, which aremore expensive but which give access to polyurethanes exhibiting:

[0069] better resistance to UV radiation,

[0070] a more stable color,

[0071] excellent behavior when used externally.

[0072] The action of primary alcohols gives carbamates which are verystable thermally in comparison with aromatic isocyanates.

[0073] Methanol was chosen as blocking agent for the alkyl isocyanate.This is because this alcohol is inexpensive, has a low molecular massand has a limited toxicity.

[0074] A limitation on VOCs is promoted by such a blocking agent incomparison with the other agents. This methodology clearly falls withinthe scope of the development of a cleaner chemistry, an approach favoredby current research.

[0075] Reactants Involved

[0076] The alkyl isocyanate chosen is hexyl isocyanate. It is blockedvery simply with methanol with conventional heating for 4 hours. Thereaction results in the formation of N-hexyl methyl urethane, which willbe used as starting reactant during the transcarbamation reaction.

n-hex-N═C═O+MeOH→n-hex-NH—CO—OMe

[0077] The primary alcohol chosen for carrying out the transcarbamationis octan-1-ol. The reaction of it with hexyl isocyanate withconventional heating for 4 hours results in the formation of the endproduct: N-hexyl octyl urethane.

n-hex-N═C═O+n-OctOH→n-hex-NH—CO—O-n-Oct

[0078] The characterization of this product by conventional analyticaltechniques was necessary in order to carry out kinetic monitoring of thetranscarbamation reaction by gas chromatography (retention time andresponse factor).

[0079] Kinetic Study

[0080] The transcarbamation reaction studied, carried out in the absenceof solvent and in the presence of 1 mol % of catalyst (in order to havea rapid reaction), is represented diagrammatically below:

[0081] Carba 1: 3.14 mmol (500 mg)

[0082] OctOH: 1 eq. or 10 eq.

[0083] Internal reference (hexadecane): 0.5 eq.

[0084] Cat.: 1 mol %.

[0085] 130° C.

[0086] Kinetic Results of Various Catalysts Tested Catalyst k in mol⁻¹ ·l · min⁻¹ Yield (%) Bu₂Sn(laurate)₂ reference 1.10 · 10⁻³ 26Bu₂Sn(2-ethylhexanoate)₂ 7.32 · 10⁻⁴ 27 comparativeBuSn(2-ethylhexanoate)₃ 3.34 · 10⁻⁴ 15 comparative Bu₂SnCl₂ 9.73 · 10⁻⁴34 Bu₂Sn(OMe)₂ comparative 5.18 · 10⁻⁴ 17 Bu₂SnCl(OAc) 2.30 · 10⁻³ 53Bu₂SnBr(OAc) 2.57 · 10⁻³ 55 Bu₂Sn(NCS)₂ 3.10 · 10⁻³ 63

[0087] As regards the control catalysts, such as dibutyltin diacetateand dibutyltin dilaurate, the latter display a very mediocre catalyticactivity with yields at the end of the reaction of 43 and 26%respectively. Subsequently, a series of compounds comprising analkanoate, halogen and methoxy ligand is observed, which compoundsexhibit a relatively low effectiveness. The mixed halogen/acetatecompounds show an excellent catalytic activity with good yields at theend of the reaction. However, these compounds are in fact mixturesbetween the tin(IV) compound and corresponding symmetrical and mixeddistannoxanes. It will be seen below that the latter are very effective.Finally, dibutyltin diisothiocyanate proves to be the most activecompound in this table with a rate constant of 3.10·10⁻³ mol⁻¹·l·min⁻¹and a final yield of 63%.

[0088] Catalysts Based on Distannoxanes Catalyst k in mol⁻¹ · l · min⁻¹Yield (%) [(AcO)Bu₂Sn]₂O 1.39 · 10⁻³ 42 [ClBu₂Sn]₂O 1.84 · 10⁻³ 51[(NCS)Bu₂Sn]₂O 3.54 · 10⁻³ 62 [BrBu₂Sn]₂O 5.10 · 10⁻³ 68 [BrBu₂Sn]₂O(0.5 mol) 2.93 · 10⁻³ 65 [BrBu₂Sn]₂O (Amounts*10) 2.48 · 10⁻³ 59(AcO)Bu₂Sn—O—Zn—OC₅H₁₁ 1.12 · 10⁻³ 39

[0089] In the context of the transcarbamation reaction, compounds ofthis type also prove to be outstandingly effective.1,3-Dibromotetrabutyldistannoxane proves to be the most effective here,with a rate constant of 5.10·10⁻³ mol⁻¹·l·min⁻¹ and a final yield of68%. It should be noted that, even used at 0.5 mol % or with amounts ofreactants 10 times greater, the results are still as good.

[0090] Nevertheless, it turns out that this type of compound results inthe formation of a not insignificant amount of isocyanate in thereaction medium.

1. Use as transcarbamation catalyst of compounds corresponding to thefollowing general formula (I):

where: X′ is chosen from chloride, bromide, iodide or thiocyanateradicals or sulfonate radicals, advantageously perfluorinated on thecarbon carrying the sulfonate functional group; X is chosen from thevalues of X′ and from radicals of formula Y-Z; Y is chosen from thegroup of chalcogens, advantageously light chalcogens (that is to say,oxygen and sulfur); Z is chosen from the group consisting oftrisubstituted tin, monosubstituted zinc and residues ofoxygen-comprising acids, the OH functional group not being included. 2.The use as claimed in claim 1, characterized in that X has the samevalue as X′.
 3. The use as claimed in claims 1 and 2, characterized inthat at least one of the X or X′ groups is chosen from halides andthiocyanates.
 4. The use as claimed in claim 1, characterized in that Zhas the same value as:


5. A composition, characterized in that it comprises at least onecarbamate capable of being obtained by the reaction of a hydroxylatedcompound with an advantageously aliphatic isocyanate and at least onecompound of following general formula (I):

where: X′ is chosen from chloride, bromide, iodide or thiocyanateradicals or sulfonate radicals, advantageously perfluorinated on thecarbon carrying the sulfonate functional group; X is chosen from thevalues of X′ and from radicals of formula Y-Z; Y is chosen from thegroup of chalcogens, advantageously light chalcogens (that is to say,oxygen and sulfur); Z is chosen from the group consisting oftrisubstituted tin, monosubstituted zinc and residues ofoxygen-comprising acids, the OH functional group not being included. 6.The composition as claimed in claim 5, characterized in that itadditionally comprises an alcohol or polyalcohol which is advantageouslyprimary.
 7. The composition as claimed in claims 5 and 6, characterizedin that said hydroxylated compound is chosen from alcohols which arevolatile at a temperature at least equal to 150° C. and fromhydroxylated masking agents.
 8. The composition as claimed in claims 5to 7, characterized in that said hydroxylated compound is methanol. 9.The composition as claimed in claims 5 to 7, characterized in that saidhydroxylated compound is chosen from masking agents, advantageously fromphenols and oximes.
 10. A transcarbamation process, characterized inthat use is made, as transcarbamation catalyst, of the compounds offormula (I):

where: X′ is chosen from chloride, bromide, iodide or thiocyanateradicals or sulfonate radicals, advantageously perfluorinated on thecarbon carrying the sulfonate functional group; X is chosen from thevalues of X′ and from radicals of formula Y-Z; Y is chosen from thegroup of chalcogens, advantageously light chalcogens (that is to say,oxygen and sulfur); Z is chosen from the group consisting oftrisubstituted tin, monosubstituted zinc and residues ofoxygen-comprising acids, the OH functional group not being included. 11.The process as claimed in claim 10, characterized in that thetranscarbamation reaction is carried out at a temperature of between 100and 200° C., advantageously between 120 and 180° C.